Opioid dependence is a chronic, recurrent disorder with periods of stabilization during treatment and frequent relapse into chronic use. While attendant crime is of primary social concern, because of injection practices and other lifestyle characteristics, opioid addicts are at elevated risk of mental health conditions, premature mortality, and HIV and other communicable diseases. Methadone Maintenance Treatment (MMT) has been found to be the most effective form of treatment for opioid dependence. The availability of treatment slots, the means by which MMT is delivered, and availability of ancillary services to address co-morbid health conditions varies greatly locally and internationally. Accordingly, the accessibility, comprehensiveness and quality of individual drug treatment practices have important public health implications that require evaluation. The behavioral benefits and economic merits of maximizing access to MMT are well-established;increased access to quality MMT may also help contain the spread of HIV among injection drug users. Differences in drug treatment and criminal justice policies in California (CA) and British Columbia (BC) likely result in different health and economic outcomes for opioid dependent individuals in these jurisdictions. Our broad objective is to quantify these differences within a comprehensive model to determine the effects of actual and simulated policies and practices and how they are manifested in the long-term in these contrasting regions. CA and BC make for an informative comparison in US-Canadian drug policy;both regions feature among the largest per capita populations of opioid dependent individuals in their countries and both feature progressive drug treatment policies relative to other states or provinces. Comparing the types of individuals accessing treatment, their treatment outcomes and the costs they incur on the criminal justice and health systems will contribute to fitting a simulation model explicating the differences in health outcomes and costs over the lifetime of a representative cohort of opioid dependent patients presenting for MMT in CA versus BC. Simulation modeling provides the advantage of being able to determine how specific policies and practices impact health benefits and costs holding other factors constant. The respective drug treatment systems and the policies shaping them will be described through a series of state/province- level individually-linked administrative databases on drug treatment and other health resource utilization, arrests and other criminal justice system involvement, and vital statistics. With two disparate treatment and criminal justice systems being modeled using population-level administrative data, key features of each system can be altered one-at- a-time or jointly to determine and disentangle the expected effect of hypothetical policy changes. A range of specific parameter values can be modified to examine their potential effects in the comparator regions. Inputs from the CA and BC systems such as duration of retention in treatment and differential probability of arrest and incarceration may be exchanged in the regions to quantify differences in health and economic outcomes as a result of specific aspects of the treatment systems. Similarly, other parameters including differences in the incidence of infectious diseases such as HIV can also be modeled, thus providing greater contextual information on specific aspects of public health significance. We expect that the model can subsequently be used as a tool by these and other jurisdictions to study hypothetical effects of policy changes on opioid treatment systems, intervention effects, and the clients they serve. PUBLIC HEALTH RELEVANCE: Our ultimate objective is to determine whether further health and economic benefits may be gained as a result of modifying drug treatment policies and practices in CA and BC. We hypothesize that savings in government revenues may result from many of the hypothetical policy changes considered. These savings could be reinvested into more effective and productive endeavors in drug treatment, criminal justice, healthcare or other sectors. We expect to deliver empirical support for this perspective and to provide an evidence based and decision-making tool for government administrative bodies to help shape policies on drug dependence that promote economic allocative efficiency and the health and well-being of opioid-dependent individuals.